This invention relates to multi-contact rotary switches, and particularly to switches of the type in which cam lobes on a rotatable member are arranged to selectively control a plurality of circuits by causing independently operable switch contact elements to move into and out of their circuit-closing positions.
Many multi-contact rotary switches have been designed, but none have been found to meet the requirements which led to the present invention. The purpose is to develop a compact rotary switch which will be well suited for use as a range/function switch in digital multimeters and like instruments. There are at least three important goals in developing such a switch:
a. It should minimize manufacturing costs by utilizing a minimum number of parts which lend themselves to efficient manufacturing methods; PA1 b. It should be very compact relative to the number of switching circuits provided; and PA1 c. It should be highly efficient and reliable in accomplishing its switching functions, which requires that it have high voltage breakdown capability, both from switch to switch and also between the terminals of cooperating switch elements. PA1 a. A center cam rotor having cam tracks, or lobes, on both sides is mounted between two identical side members, or switch blocks, which each carry a plurality of switches separately actuated by the cam tracks; PA1 b. The side members laterally (axially) confine the cam rotor by providing bearing surfaces which engage the cam rotor; PA1 c. Each side member, or switch block, has two diametrically spaced banks of switches, the switches in each bank being actuated by half of the cam tracks to compensate for the greater acceptable density of cam track locations; PA1 d. The movable element of each switch element pair is laterally confined in a groove, or channel, to insure proper alignment; and PA1 e. The movable element of each switch element pair is so designed as to provide substantial flexing after switch engagement, thereby insuring positive contacting force and contact wiping action.
The separate Prior Art Statement lists the patents found in a novelty search. Of those, two appear to be useful in defining the background of the present invention. Edwards U.S. Pat. No. 3,845,256 discloses a cam-operated timer switch having in combination (note FIG. 4): (a) a disc-shaped timing cam having on its side face a plurality of concentrically disposed, radially spaced arcuate cam tracks, and (b) a plurality of switches operated individually by separate cam tracks, each switch combining a stationary contact and a flexible blade engageable with the stationary contact under control of the aligned cam track. Gerhardt U.S. Pat. No. 2,586,797 shows a printed circuit timer which combines (see FIGS. 5, 6 and 9) modular housing units, modular current selector means, and modular timing circuit boards to simplify design and fabrication of the timer.